The present invention relates to a semiconductor device which surely protects the integrated circuit of its semiconductor chip, provides a stable electrical connection between its external system and semiconductor chip, and realizes denser mounting of the semiconductor chip on its substrate, and it also relates to a method of manufacturing the same. With the semiconductor device of the present invention, the miniaturization of data communication equipment, office electronic equipment, home electronic appliances, industrial electronic equipment such as a measuring apparatus and assembly robot, medical electronic equipment, and electronic toys will easily be realized.
Below, a conventional semiconductor device will be described with reference to the drawings.
FIG. 11 shows the cross-sectional structure of the semiconductor device which is called a quad flat package (QFP). In the conventional semiconductor device shown in FIG. 11, its external terminals are provided on the side faces of the semiconductor package.
In a concave portion 3 of the semiconductor package 2, which serves as an insulating substrate composed of a ceramic, is mounted a semiconductor chip 1 with electrodes (not shown) formed on its top surface. Around the concave portion 3 is formed a wire-bonding area 4 in which electrodes 5 are provided so as to correspond to the electrodes formed on the semiconductor chip 1. The electrodes 5 on the wire-bonding area 4 and the electrodes formed on the semiconductor chip 1 are connected by thin wires of Au or other material. To provide electrical connections between the electrodes 5 in the wire-bonding area 4 and an external system, external terminals 7 are formed on the sides of the semiconductor package 2. To protect the semiconductor chip 1 and thin wires 6, a lid 8 is attached to the semiconductor package 2.
Next, a method of manufacturing the conventional semiconductor device will be described with reference to the drawings. FIGS. 12 to 14 are cross sections which illustrate the process steps of manufacturing the conventional semiconductor device according to the method.
The method of manufacturing the conventional semiconductor device consists of a dice-bonding process, wire-bonding process, and sealing process.
First, the dice-bonding process will be described with reference to FIG. 12. In this process, the semiconductor chip 1 is mounted in the semiconductor package 2 by bonding the semiconductor chip 1 to the concave portion 3 of the semiconductor package 2 with the use of a conductive adhesive (low-melting-point glass with Ag, or Au--Si eutectic material). The process is performed by using an apparatus called dice bonder.
Next, the wire-bonding process will be described with reference to FIG. 13. To provide electrical connections between the electrodes of the semiconductor chip 1 mounted in the semiconductor package 2 and the electrodes 5 provided in the wire-bonding area 4 of the semiconductor package 2, these electrodes are connected by the thin wires 6 of Au (gold) or Al (aluminum). The process is performed by using an apparatus called wire bonder.
Finally, the molding process will be described with reference to FIG. 14. After connecting the electrodes of the semiconductor chip 1 to the electrodes 5 of the semiconductor package 2 by the thin wires 6 of Au or Al, the semiconductor package 2 is molded with the lid 8 so that the concave portion 3 of the semiconductor package 2 is covered with the lid 8. The lid 8 is attached to the semiconductor package 2 by means of an adhesive, a soldering, an Au--Sn alloy or by a resistance pressure welding method.
The semiconductor packages for the semiconductor device which have conventionally been used can be roughly divided into the following two types.
The first type is ceramic packages. The ceramic packages can be subdivided into a lamination-type package and a glass-molding ceramic package.
The lamination-type ceramic package is formed as follows: first, minute holes are formed by mechanical processing in specified positions of green sheets, which are necessary for wiring. Those holes are filled with a conductive past. Next, a circuit is formed by the printing on each green sheet so that the green sheets with printed circuits are stacked one after the other. Subsequently, the stacked green sheets are subjected to baking, resulting in the main body of the package.
The glass-molding ceramic package is formed as follows: first, a low-melting-point glass is applied onto the top surface of the main body of the package which is formed by a press forming method, as well as a lead frame is attached thereto. The lead frame is then bonded to the main body of the package by melting the low-melting-point glass in a heating furnace. After that, a Au paste or the like is applied to the central portion of the main frame of the package in which a semiconductor chip is to be mounted. Further, the main body of the package is sealed through the low-melting-point glass by means of a ceramic lid formed by the press forming method.
The second type is plastic packages, which are most commonly used. A package of this type is formed as follows: first, a semiconductor chip is mounted on a lead frame, and then an electrical connection is provided between the lead frame and semiconductor chip by a wire-bonding method. After that, a resin containing as its main component a thermo-curing resin, such as an epoxy resin, is injected into a mold, while the lead frame and semiconductor chip are held in the hollow portion of the mold, followed by curing, resulting in a plastic package.
With the ceramic and plastic packages, the electrical connection between the semiconductor chip and the package is mainly provided by a wire-bonding method using thin wires of Au or Al. However, the mounting technique using the wire-bonding method is disadvantageous in that the degree of miniaturization of the package is limited, for it requires a wiring area for connecting wires to be formed around the semiconductor chip which is mounted in the main portion of the package.
There has also been proposed a package formed by using a flip-flop mounting technique which was developed in order to mount a semiconductor chip directly on a circuit board. In a package formed by using the flip-flop mounting technique, a ceramic or a resin is used as the material for forming the substrate of the package.
The configuration which is characteristic of a conventional package formed by the flip-flop mounting technique is a cavity in which a semiconductor chip is to be mounted, similarly to the conventional ceramic package formed by the wire-bonding method. To protect the semiconductor chip mounted in the package, a lid composed of a metal, ceramic, or other material should therefore be attached to the package by using as a bonding material a low-melting-point glass or an Au--Sn alloy or by the method of resistance welding.
As the degree of miniaturization and performance of electronic equipment has been increasing, the main body of the semiconductor package described above is also required to be smaller and thinner, while its external electrodes are required to be greater. The semiconductor package described above is also provided with a heat sink for radiation heat generated from the semiconductor chip.
Although the conventional semiconductor device shown in FIG. 11 is so constituted as to correspond to the miniaturization of the wiring layers of the semiconductor package 2, to the multiplied directions of the external terminals 7, and to the reduction of the spacing between the external terminals 7, the wire-bonding method is commonly used to provide an electrical connection between the semiconductor chip 1 and the semiconductor package 2 thereof. Hence, it is necessary, in general, in the semiconductor package 2 to surround the semiconductor chip 1 with an area having the width of 2.0 mm or more in which the electrodes 5 are to be formed so that the thin wires 6 are connected thereto. In addition, it is also necessary to surround the wire-bonding area 4 with an area having the width of 2.0 mm or more to which the lid 8 is to be attached.
Therefore, it is impossible to reduce the area of the semiconductor package 2 to the order of the area of the semiconductor chip 1, so that the requirements on the reduced size and thickness of the semiconductor package 2 cannot be fulfilled.
As for the method of mounting the semiconductor chip directly on the circuit board without holding the semiconductor chip in the semiconductor package, which has been proposed in order to densely mount the semiconductor chip on the circuit board, a heat sink should be provided so as to absorb heat generated from the semiconductor chip, with the result that a thinner semiconductor device cannot be realized, either.